Semiconductor light emitting device, semiconductor light emitting apparatus, and method of manufacturing semiconductor light emitting device

ABSTRACT

Disclosed is a semiconductor light emitting device comprising: a substrate having first and second major surfaces and being translucent to light in a first wavelength band; and a semiconductor stacked body provided on the first major surface and including a light emitting layer that emits light in the first wavelength band. A side face of the substrate has a recess. A cross section located between the first and second major surfaces is substantially smaller than the first and second major surfaces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2005-060276, filed on Mar. 4,2005; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to a semiconductor light emitting device, asemiconductor light emitting apparatus, and a method of manufacturing asemiconductor light emitting device, and more particularly to asemiconductor light emitting device and a method of manufacturing thesame in which the external light extraction efficiency is improved.

There is an increasing demand for higher brightness of semiconductorlight emitting apparatuses in various applications such as backlights ofliquid crystal displays, push button lamps of mobile phones, andlighting substituted for fluorescent lamps. In order to obtain highbrightness while reducing power consumption, it is important to improvethe external light extraction efficiency of a semiconductor lightemitting device.

In a semiconductor light emitting device, the light emitted from itsactive layer can be extracted outside without multiple reflection onlywhen the incident angle to the radiating surface is smaller than thecritical angle. A semiconductor light emitting device having anradiating surface made of GaP (having a refractive index of about 3.3)and sealed in epoxy-based sealing resin (having a refractive index ofabout 1.5) has a critical angle of about 27 degrees. The light having anincident angle greater than the critical angle at the side face of thesemiconductor light emitting device is either radiated outside aftermultiple reflection inside the device, or absorbed inside to result inineffective light.

A structure for improving the external light extraction efficiency of asemiconductor light emitting device is disclosed in which thesemiconductor light emitting device has an inclined side face to reducethe incident angle inside the device from the light emitting layer tothe side face of the device, thereby reducing the influence of totalreflection at the side face of the semiconductor light emitting device(e.g., Japanese Laid-Open Patent Application 2003-188410).

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided asemiconductor light emitting device comprising:

a substrate having first and second major surfaces and being translucentto light in a first wavelength band; and

a semiconductor stacked body provided on the first major surface andincluding a light emitting layer that emits light in the firstwavelength band,

a side face of the substrate having a recess, and

a cross section located between the first and second major surfacesbeing substantially smaller than the first and second major surfaces.

According to other aspect of the present invention, there is provided asemiconductor light emitting apparatus comprising:

a packaging member;

a semiconductor light emitting device mounted on the packaging member;and

sealing resin sealing the semiconductor light emitting device,

the semiconductor light emitting device including:

-   -   a substrate having first and second major surfaces and being        translucent to light in a first wavelength band; and    -   a semiconductor stacked body provided on the first major surface        and including a light emitting layer that emits light in the        first wavelength band,    -   a side face of the substrate having a recess, and    -   a cross section located between the first and second major        surfaces being substantially smaller than the first and second        major surfaces.

According to other aspect of the present invention, there is provided amethod of manufacturing a semiconductor light emitting devicecomprising:

forming, on a first major surface of a substrate having first and secondmajor surfaces and being translucent to light in a first wavelengthband, a semiconductor stacked body including a light emitting layer thatemits light in the first wavelength band;

forming a reformed layer inside the substrate by moving a laser beamrelative to the substrate while converging and applying the laser beamto the substrate to cause multiphoton absorption near a focus;

separating the substrate along the reformed layer; and

etching away the reformed layer exposed at a side face in response toseparation of the substrate to form a recess.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a semiconductor light emittingdevice according to a first embodiment of the invention as viewed fromobliquely above;

FIG. 2 is a schematic cross-sectional view of a semiconductor lightemitting device according to the first embodiment of the invention;

FIG. 3 is a schematic cross-sectional view of a semiconductor lightemitting device of a comparative example;

FIG. 4 is a schematic cross-sectional view of a semiconductor lightemitting device according to a second embodiment of the invention;

FIGS. 5 to 10 are process cross-sectional views showing a process ofmanufacturing a semiconductor light emitting device according to thesecond embodiment of the invention;

FIG. 11 is a schematic view showing the process of forming a reformedlayer 44 in more detail;

FIG. 12 is a schematic cross-sectional view of a semiconductor lightemitting device according to a third embodiment of the invention;

FIG. 13 is a schematic cross-sectional view of a semiconductor lightemitting device according to a fourth embodiment of the invention; and

FIG. 14 is a schematic cross-sectional view of a semiconductor lightemitting apparatus using a semiconductor light emitting device accordingto the first embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will now be described with reference to thedrawings.

FIGS. 1 and 2 are schematic views illustrating a semiconductor lightemitting device according to a first embodiment of the invention. Morespecifically, FIG. 1 is a schematic perspective view of a semiconductorlight emitting device according to this embodiment as viewed fromobliquely above. FIG. 2 is a schematic view illustrating thecross-sectional structure of a semiconductor light emitting deviceaccording to this embodiment.

The semiconductor light emitting device 70 of this embodiment has astructure comprising a substrate 10 transparent to the light radiatedfrom the semiconductor light emitting device 70 (the term “transparent”used herein is intended to imply not only no absorption of light emittedfrom the light emitting layer, but also partial transmission of thelight with some absorption) on which a semiconductor stacked body 19including an active layer 14 (i.e., the light emitting layer) is formed.An upper electrode 20 is provided on top of the semiconductor stackedbody 19. On the other hand, as illustrated in FIG. 2, a lower electrode22 is provided under the transparent substrate 10. It should be notedthat the lower electrode 22 is not shown in FIG. 1 because it is hiddenunder the transparent substrate 10.

The semiconductor stacked body 19 has a structure comprising, forexample, a first cladding layer 12 on which the active layer 14, asecond cladding layer 16, and a current diffusion layer 18 are stackedin this order.

A recess 28 is formed on the side face of the transparent substrate 10of the semiconductor light emitting device 70 according to thisembodiment. The recess 28 is provided so that the cross section locatedbetween the upper and lower major surfaces of the transparent substrate10 is substantially smaller than these upper and lower major surfaces.In an example shown in FIGS. 1 and 2, the recess 28 is composed of afirst plane 24 extending obliquely downward and a second plane 26extending obliquely upward. Part of the light emitted from the activelayer 14 that is directed to the underlying transparent substrate 10 isradiated outside from the side face of the transparent substrate 10. Inthis case, since the recess 28 is formed on the side face, more of thelight emitted from the active layer 14 is extracted outside through therecess 28. The recess 28 serves to improve the light extractionefficiency as described later in detail.

Next, components of the semiconductor light emitting device of thisexample will be described more specifically.

The transparent substrate 10 is selected to be made of n-type GaPmaterial, for example. The first cladding layer 12 is selected to be ann-type InAlP film, the active layer 14 is an InGaAlP film, the secondcladding layer 16 is a p-type InAlP film, and the current diffusionlayer 18 is a p-type GaP film. These constitute the semiconductorstacked body 19. A p-type, upper electrode 20 (made of Au, Au alloy, orthe like) is formed partially on top of the current diffusion layer 18.An n-type, lower electrode 22 (made of Au, Au alloy, or the like) isformed partially on the lower side of the transparent substrate 10. Thelower electrode 22 is mounted, for example, on a lead of a package usingAuSn solder, silver paste, or the like.

The semiconductor stacked body 19 and the transparent substrate 10 arebonded together by the wafer bonding process and the like. In this case,preferably, a bonding layer made of GaP or the like is providedtherebetween. In addition, a contact layer can be provided between thecurrent diffusion layer 18 and the upper electrode 20 to further reducethe contact resistance.

Visible light is emitted from the InGaAlP active layer 14. Sinceabsorption of visible light within the GaP substrate is as small as 20%or less, a higher external light extraction efficiency is obtained ascompared to the GaAs substrate.

The foregoing refers to an example of In_(x)Ga_(y)Al_(1-x-y)P-basedmaterial (where (x+y)≦1, 0≦x≦1, 0≦y≦1). In addition, for example,In_(z)Ga_(w)Al_(1-z-w)N-based material (where (z+w)≦1, 0≦z≦1, 0≦w≦1) orthe like may be used. Sapphire or the like may also be used for thetransparent substrate.

Next, the effect of the recess 28 will be described with reference toFIG. 2 using the light emitted from point P1 in the active layer 14 asan example. In this figure, arrows L5 and L6 represent the lightdirectly radiated upward (i.e., light extraction side) from the activelayer 14.

Light L1 from the light emitting point P1 is reflected by the lowerelectrode 22 and incident on the second plane 26. The light L1 having anincident angle smaller than the critical angle θc is not reflected bythe second plane 26 and becomes radiated light.

Light L2 incident on the first plane 24 becomes direct emission lightwhen its incident angle is smaller than the critical angle θc. The term“direct emission light” used herein refers to the light that is emittedfrom the active layer 14, passed through the transparent substrate 10,and directly radiated outside. That is, the light is directly radiatedoutside without being reflected within the chip by the side face andlower face of the transparent substrate 10, the lower electrode 22, andthe like. The region where direct emission occurs is referred to as“direct emission region” 82, and illustrated by dots. Similarly, adirect emission region 84 is illustrated by dots where direct emission,as typified by light L3, occurs between the first plane 24 and thesemiconductor stacked body 19. In the vicinity of the lower electrode22, alloying between the electrode metal 22 and the transparentsubstrate 10 results in some decrease of reflectance. However, ourprototypes exhibited a reflectance of about 50%. When the transparentsubstrate 10 is made of GaP (having a refractive index of about 3.3) andthe semiconductor light emitting device 70 is sealed in epoxy resin(having a refractive index of about 1.5), the critical angle θc is about27 degrees.

On the other hand, light L4 emitted from the light emitting point P1 andreflected by the lower electrode 22 is radiated from the second plane 26of another recess 28. When the depth D1 of the recess 28 is increased,the light reflected by the lower face of the transparent substrate 10and then radiated outside (e.g., light L1) is decreased while the lightdirectly radiated from the recess 28 (e.g., light L2) is increased. Thedepth D1 of the recess 28 can be appropriately determined to increasethe external light extraction efficiency and to maintain the mechanicalstrength of the chip. As an example, in a transparent substrate 10measuring 150 to 1000 micrometers per side, the depth D1 desirablyranges from 2 to 100 micrometers. Relevant structural parameters includethe size of the active layer 14, the distance between the active layer14 and the substrate, and the thickness of the substrate. It is thusdesirable to determine the shape of the recess 28 (including the depthD1) based on simulations or experiments. According to prototyping by theinventor, the angle θ1 between the first plane 24 and the horizontalplane desirably ranges from 10 to 80 degrees. On the other hand, theangle θ2 between the second plane 26 and the horizontal plane desirablyranges from 10 to 80 degrees.

Next, the effect of the recess 28 in this embodiment will be describedin more detail with reference to a comparative example investigated bythe inventor.

FIG. 3 is a schematic cross-sectional view of a semiconductor lightemitting device 70 of a comparative example. With regard to this figure,the elements similar to those described above with reference to FIGS. 1and 2 are marked with the same reference numerals and will not bedescribed in detail. The transparent substrate 10 of this comparativeexample has a side face composed of four planes vertical to the lowerelectrode 22.

When the transparent substrate 10 is made of GaP and the semiconductorlight emitting device 70 is sealed in epoxy-based resin, the criticalangle θc is about 27 degrees. In FIG. 3, the light H5 and H6 representdirect emission light from the active layer 14.

In the direct emission region 88 where the incident angle to thevertical side face 30 is smaller than the critical angle θc, light H3from point P2 is directly radiated outside. On the other hand, light H1is reflected by the lower electrode 22 and then incident on the verticalside face 30. In this situation, the light having an incident anglegreater than the critical angle θc is totally reflected by the verticalside face 30 as illustrated in FIG. 3. Then the light has an increasedoptical length due to multiple reflection and is incident on the activelayer 14 to increase optical absorption, which decreases the amount oflight that can be extracted outside. In contrast, the light L1 in thefirst embodiment, as compared to the light H1, is radiated from therecess 28.

Moreover, light H7 incident on the vertical side face 30 at an anglegreater than the critical angle is totally reflected, and furtherreflected by the lower electrode 22 (double reflection). If it returnsto the active layer 14, the amount of light that can be extracted isdecreased due to absorption by the active layer 14. Light H2, which hasan incident angle greater than the critical angle θc and smaller thanthat of the light H7 is totally reflected by the vertical side face 30,further reflected by the lower electrode 22, and incident on anothervertical side face 30. Then, if the incident angle is smaller than thecritical angle θc, the light is radiated outside as illustrated in FIG.3. In this case, the light is subjected to double reflection inside, andparticularly to optical absorption by reflection at the lower electrode22. In contrast, the light L2 in the first embodiment, as compared tothe light H2, is direct emission light without double reflection.

Furthermore, light H4 is reflected by the lower electrode 22, andfurther totally reflected by the vertical side face 30 toward the insideof the chip. As a result, part of the light is difficult to extractoutside. In contrast, the light L4 in the first embodiment, as comparedto the light H4, is radiated outside from the recess 28, although it isreflected once by the lower electrode 22.

In general, optical loss in a semiconductor light emitting device iscaused by reabsorption in the active layer, absorption by the alloylayer in the electrode region, intracrystalline absorption includingfree carrier absorption in the doped region, and the like. Therefore,while the direct emission light without internal reflection involves asmall loss, any reflection increases the loss as described above. Thatis, multiple reflection decreases the external light extractionefficiency by the above causes in conjunction with the increase ofoptical length.

In addition, if the light is subjected to many internal reflections, itis radiated in directions different from the light extraction side.Therefore, often, the light cannot be effectively extracted outside thefinally packaged semiconductor light emitting apparatus.

As described above, in the comparative example illustrated in FIG. 3,total reflection occurs in a wide area of the side face of the device.On the contrary, in the first embodiment where, for example, recesses 28having a depth D1 of 2 micrometers or greater are formed, the area ofcausing total reflection can be reduced on the side face of the device.As a result, the direct emission light can be increased. In addition,the number of multiple reflections inside the semiconductor lightemitting device can be reduced, which in turn can reduce opticalabsorption. Consequently, in a semiconductor light emitting apparatususing a surface mount package described below, the present embodimentachieves an external light extraction efficiency of 1.4 to 1.7 timesgreater as compared to the apparatus using the semiconductor lightemitting device of the comparative example illustrated in FIG. 3.Moreover, the inclined side face is limited to the recess 28 havingdepth D1, which enables improvement of external light extractionefficiency without increasing the chip size. In other words, the lightextraction efficiency can be improved while maintaining the total numberof chips per wafer at the level in the case of rectangular chips.

This embodiment has another advantageous effect that the area of theupper and lower faces of the semiconductor light emitting device can bemade substantially equal.

More specifically, the light emitting diode chip disclosed in JapaneseLaid-Open Patent Application 2003-188410 cited above as a comparativeexample has inclined side faces to be shaped as a truncated pyramid inorder to improve light extraction efficiency. However, in the structureof this comparative example, the area of the horizontal plane above theinclined side face is smaller than the area of the bottom face below theside face. Since the area of the electrode provided on the upper facehas a lower bound in order to avoid increasing the contact resistance,the chip size for obtaining the same optical output is increased ascompared to the structure in which the upper and lower faces have anequal area. This result in a problem of decreasing the total number ofchips obtained per wafer. In addition, if the chip of this comparativeexample is mounted upside down, the area of the mounting surface issmaller than the area of the upper face of the device. Thus thedecreased bonding area lowers the bonding strength and physicalstability.

On the contrary, in the semiconductor light emitting device according tothis embodiment, the upper and lower major surfaces of the device have asubstantially equal area. Therefore, advantageously, the number of chipsobtained per wafer is not decreased, and the device can be bonded in astable and secure manner. As a result, the device can provide athermally and mechanically superior structure and achieve higherreliability in spite of its inclined side faces.

Next, a semiconductor light emitting device according to the secondembodiment will be described.

FIG. 4 is a schematic cross-sectional view of a semiconductor lightemitting device 70 according to the second embodiment. With regard tothis figure, the elements similar to those described above withreference to FIGS. 1 and 2 are marked with the same reference numeralsand will not be described in detail.

In this embodiment, the side face of the transparent substrate 10 has acurved recess 32. Again, the recess 32 is provided so that the crosssection located between the upper and lower major surfaces of thetransparent substrate 10 is substantially smaller than these upper andlower major surfaces. The curved recess 32 is composed of a curveconcave on the outside in the cross section shown in FIG. 4. Specificexamples include semielliptic and semicircular cylinder surfaces. Inthis case again, for example, the transparent substrate 10 may be madeof n-type GaP, and the semiconductor light emitting device 70 may besealed in epoxy resin.

Light G5 and G6 from light emitting point P3 in the active layer 14 aredirect emission light from the active layer 14. Light G1 from the lightemitting point P3 is reflected by the lower electrode 22 and thenradiated outside from the recess 32. In the recess 32, incident lightsuch as light G2 is directly radiated outside in the direct emissionregion 92 marked with dots where the incident angle to the tangent planeat an incident point on the recess 32 is smaller than the critical angleθc. In the direct emission region 94 marked with dots between the recess32 and the semiconductor stacked body 19, light G3 having an incidentangle smaller than the critical angle θc is directly radiated outside.

Light G4 from the light emitting point P3 is reflected by the lowerelectrode 22 and then radiated outside from another recess 32. Theeffect of the curved recess 32 shown in FIG. 4 is understood similarlyto that of the planar recess 28 of the first embodiment.

The second embodiment can also expand the region where the light fromthe active layer 14 can be directly extracted outside without reflection(regions 92 and 94 illustrated by dots). Again, with respect to thelight reflected by the lower electrode 22 (e.g., G4), the number ofmultiple reflections can be decreased. Consequently, the presentembodiment achieves an external light extraction efficiency of 1.4 to1.7 times that of the comparative example. In addition, as with thefirst embodiment, the light extraction efficiency can be improvedwithout increasing the chip size. Moreover, in the second embodiment,the recess 32 is composed of a curved surface. As a result, theradiation angle of light can be continuously varied. Therefore thedirectional characteristics of the semiconductor light emittingapparatus can be smoothly varied.

In a transparent substrate 10 measuring 150 to 1000 micrometers perside, the depth D2 of the recess 32 desirably ranges from 2 to 100micrometers.

Next, the method of manufacturing a semiconductor light emitting deviceaccording to the second embodiment will be described.

FIGS. 5 to 10 are process cross-sectional views showing the method ofmanufacturing a semiconductor light emitting device of this embodiment.

FIG. 5 is a schematic cross-sectional view at the end of the waferprocess. A semiconductor stacked body 19 including an active layer 14(i.e., light emitting layer) is provided on a transparent substrate 10by crystal growth or bonding. Subsequently, an upper electrode 20 and alower electrode 22 are patterned on the upper face of the semiconductorstacked body 19 and on the lower face of the transparent substrate 10,respectively. In addition, part of the semiconductor stacked body 19 isetched by wet etching, RIE (Reactive Ion Etching), or the like toseparate individual chips, which completes the wafer process.

Next, the semiconductor stacked body 19 and the upper electrode 20 arecovered with mask material 40 such as resist. Then, for example, it isthree-dimensionally scanned with a beam 46 of a short-pulse-driven highpower laser such as a femtosecond laser.

FIG. 6 is a schematic cross-sectional view of the transparent substrate10 in which first reformed layers 44 are formed by three-dimensionallyscanning the region to be served as a recess. When the transparentsubstrate 10 in the semiconductor light emitting device 70 measures 150to 1000 micrometers per side, the size of the first reformed layer 44can be selected within the range of a vertical length of 2 to 150micrometers and a horizontal width of 4 to 200 micrometers.

FIG. 11 is a schematic view showing the process of forming a reformedlayer 44 in more detail.

More specifically, laser light in a wavelength band to which thesubstrate 10 is generally transparent is converged by an optical system55 to form a beam 46, which is focused at the inside of the substrate10. This results in “multiphoton absorption”, which is an opticallydamaging phenomenon that occurs when the intensity of laser light isextremely increased.

Typically, the multiphoton absorption phenomenon occurs even intransparent material when it is irradiated with a high-energy laserbeam. This phenomenon causes variation in the internal structure of thematerial, such as weakening the internal bonding of the crystal andchanging the refractive index. As a result, the bonding in the crystalbecomes fragile at the focus 46F of the high-energy laser beam.

The transparent substrate 10 can be scanned with the laser beam 46three-dimensionally in X, Y, and Z directions to move the laser beamfocus 46F in the transparent substrate 10. This can cause optical damageto a desired region to form a first reformed layer 44.

After the first reformed layer 44 is formed, as illustrated in FIG. 7,the region to be served as a dicing line for separating chips isthree-dimensionally scanned with the beam 46 in a similar manner to forma second reformed layer 48. Here again, the substrate 10 can besuccessively irradiated with the converged laser beam to cause opticaldamage and thereby form the second reformed layer 48.

The second reformed layer 48 is formed nearly through the transparentsubstrate 10, and its width can be selected within the range of 1 to 50micrometers. Therefore the dicing width can be reduced as compared tothat in the blade dicing process.

Subsequently, as illustrated in FIG. 8, an adhesive tape 50 is stuck onthe rear face of the wafer, and then the adhesive tape 50 is stretched.Since the second reformed layer 48 is made fragile, the wafer isseparated into individual semiconductor light emitting devices 70 by thestretching action.

The first reformed layer 44 exposed on the side face of the substrate 10at this time is fragile similarly to the second reformed layer 48, andthus has a faster etching rate than the other regions. Therefore, forexample, chemical including hydrochloric acid, sulfuric acid, orhydrofluoric acid, or its mixture with hydrogen peroxide can be used forwet etching to selectively remove the reformed layers 44 and 48, therebyforming the recess 32.

Instead of the wet process, a dry etching process such as CDE (ChemicalDry Etching) may also be used to form the recess 32.

Instead of forming the reformed layer by laser beam scanning, a bowingprocess by RIE may also be used to form a curved recess 32. However, ifthe reformed layer 44 is not formed, the cross-sectional shape of therecess 32 is controlled by the chemical reaction during the bowingprocess. This makes the shape control slightly difficult.

Finally, as illustrated in FIG. 10, the mask material 40 is peeled off,and then the adhesive tape 50 is removed. As a result, a semiconductorlight emitting device 70 is obtained.

In the above process illustrated in FIGS. 6 to 10, the mask material 40is provided to cover the semiconductor stacked body 19, and the adhesivetape 50 is stuck on the opposite side of the transparent substrate 10.Conversely, the adhesive tape 50 may be stuck to cover the semiconductorstacked body 19, and the mask material 40 may be provided on theopposite side of the transparent substrate 10. In this case, the laserbeam 46 is applied on the opposite side of the semiconductor stackedbody 19.

According to the manufacturing method of this embodiment, the region tobe served as a recess can be scanned with the laser beam directly in awafer. As a result, the recess 32 of a desired shape can be formed in acontrollable and productive manner. In addition, the recess 28 of thesemiconductor light emitting device 70 of the first embodimentillustrated in FIG. 1 can be similarly formed by controlling thescanning of the laser beam 46.

Next, a semiconductor light emitting device according to a thirdembodiment of the invention will be described.

FIG. 12 is a schematic cross-sectional view showing a semiconductorlight emitting device 70 according to the third embodiment. With regardto this figure, the elements similar to those in the semiconductor lightemitting device illustrated in FIG. 2 are marked with the same referencenumerals and will not be described in detail.

In the third embodiment, a rough surface 60 of minute asperities isprovided on the surface of the recess 28. More specifically, in FIG. 12,a rough surface 60 of asperities having an altitude difference T isprovided on at least a portion of at least one of the first plane 24 andthe second plane 26. An example of the rough surface 60 is illustratedin FIG. 12 in a partially enlarged view. As a supplementary remark withregard to the upper bound of the altitude difference T, the depth D1 ofthe recess 28 is selected as an upper bound because asperities can beformed if they are smaller than the depth D1.

In FIG. 12, the region in which the light emitted from light emittingpoint P4 has an incident angle to the first plane 24 smaller than thecritical angle θc is marked with dots. Without the rough surface 60 onthe first plane 24, the light in this region is directly radiatedwithout total reflection as illustrated by light M2. On the other hand,the light having an incident angle greater than the critical angle θc istotally reflected and returns inside the semiconductor light emittingdevice 70. However, the rough surface 60 provided on the first plane 24can vary the incident angle. As a result, part of the light that wouldreturn inside without the rough surface 60 can be extracted outside bydirect radiation, which can further improve the light extractionefficiency.

Similarly, a rough surface 60 provided on the second plane 26 can reducethe total reflection of light M1 emitted from the light emitting pointP4. Furthermore, it is to be understood that such a rough surface 60 maybe provided on the surface of the transparent substrate 10 other thanthe recess 28.

Next, a method of forming the rough surface 60 will be described.

For example, after the recess 32 illustrated in FIG. 9 is formed, thesubstrate stuck to the adhesive tape 50 is immersed and shaken in HF(hydrofluoric acid) at a temperature of room temperature to 70° C. forseveral to ten-odd minutes to form a rough surface 60 (frosting).Alternatively, the rough surface 60 can also be formed using gas orsolution containing fluorine. The asperities of the rough surface 60formed by these methods have an altitude difference T of severalnanometers to several micrometers. This can be smaller than the depth D1of the planar recess 28 and the depth D2 of the curved recess 32, andcan variously change the incident angle. For example, when the GaPsubstrate is etched using hydrofluoric acid, a rough surface 60 ofpyramidal asperities having a width and height of generally 1 micrometeris formed. The rough surface 60 composed of a collection of suchpyramids can increase the light extraction effect.

The third embodiment adds the improvement of light extraction efficiencyachieved by the rough surface 60 of minute asperities as described aboveto the improvement of light extraction efficiency achieved by the recessof the first and second embodiments.

Next, a semiconductor light emitting device according to a fourthembodiment of the invention will be described.

FIG. 13 is a schematic cross-sectional view showing a semiconductorlight emitting device 70 of this example. The semiconductor lightemitting device 70 is a gallium nitride based light emitting device inwhich a sapphire substrate 51 is used for the transparent substrate. AGaN buffer layer 52, n-type GaN layer 53, n-type GaN guide layer 54,active layer 55, p-type GaN guide layer 56, and p-type GaN layer 58 aregrown in this order on the sapphire substrate 51 by, for example, theMOCVD method. A p-type electrode 120 and an n-type electrode 122 areformed on the p-type GaN layer 58 and n-type GaN layer 53, respectively.Moreover, a reflector 124 for reflecting the light emitted from theactive layer is provided on the lower face of the sapphire substrate 51.A recess 28 is formed on the side face of the sapphire substrate 51using a process similar to that in the first to third embodiments. Inthis example, the driving current J of the semiconductor light emittingdevice flows between the p-type electrode 120 and the n-type electrode122, and therefore does not flow in the sapphire substrate 51.

In FIG. 13, light Q2 emitted from light emitting point P5 having anincident angle to the first plane 24 smaller than the critical angle θcis directly radiated outside. Light Q1 reflected by the reflector 124 isdirectly radiated outside from the second plane 26. As a result, thelight extraction efficiency can be improved without increasing the chipsize.

Next, a semiconductor light emitting apparatus using the semiconductorlight emitting device according to the first to fourth embodiments willbe described.

FIG. 14 is a schematic cross-sectional view of a semiconductor lightemitting apparatus according to the first embodiment.

The semiconductor light emitting device 70 is, for example, thesemiconductor light emitting device 70 according to the first to thirdembodiments. FIG. 14 illustrates use of the semiconductor light emittingdevice 70 according to the first embodiment. A first lead 100 and anopposed second lead 104 are embedded in resin 102 and 110. Thesemiconductor light emitting device 70 is bonded on the first lead 100using, for example, AuSn solder, silver paste, or the like (not shown).The upper electrode 20 provided on the semiconductor light emittingdevice 70 is connected to the second lead 104 via a bonding wire 105such as Au wire. The semiconductor light emitting device 70 and thebonding wire 105 are sealed with sealing resin 106 such as epoxy-basedresin or silicone resin. A reflector 108 is formed at the interfacebetween the resin 110 and the sealing resin 106. This structure iscalled Surface Mount Device (SMD), which allows high density packagingon a mounting board.

Light N1 and N2 are radiated approximately upward from the upper face ofthe semiconductor light emitting device 70. Light N3 radiated from thefirst plane 24 of the recess 28 of the semiconductor light emittingdevice 70 is reflected by the reflector 108, then refracted at theinterface between the sealing resin 106 and air, and radiated. Light N4from the second plane 26 is also reflected by the reflector 108, thenrefracted at the interface between the sealing resin 106 and air, andradiated. It is also the case when the recess is curved as illustratedin FIG. 4. The reflector 108 is provided by, for example, coating thesurface of the resin 110 with metal having a high reflectance such asaluminum. The external light extraction efficiency of the semiconductorlight emitting apparatus described above is 1.4 to 1.7 times greater ascompared to the semiconductor light emitting apparatus using thesemiconductor light emitting device 70 of the comparative exampleillustrated in FIG. 3.

Embodiments of the invention have been described with reference tospecific examples. However, the invention is not limited to thesespecific examples.

For example, any structure, material, shape, thickness, and arrangementof various elements including the semiconductor stacked body, the recesson the side face, minute asperities, and the package composing thesemiconductor light emitting device and semiconductor light emittingapparatus of the invention that are adapted by those skilled in the artbased on known semiconductor light emitting devices and semiconductorlight emitting apparatuses, are also encompassed within the scope of thepresent invention.

1. A semiconductor light emitting device, comprising: a substrate havingfirst and second major surfaces and being translucent to light in afirst wavelength band; and a semiconductor stacked body provided on thefirst major surface and including a light emitting layer that emitslight in the first wavelength band, a side face of the substrate havinga recess, the recess extending in parallel to the first and second majorsurfaces, the recess being formed all around the substrate, a crosssection located between the first and second major surfaces beingsmaller than the first and second major surfaces, the recess beingcomposed of a combination of a first plane extending obliquely downwardand a second plane extending obliquely upward, and the first and secondmajor surfaces having an equal size.
 2. A semiconductor light emittingdevice according to claim 1, wherein a rough surface is provided on atleast a portion of the recess.
 3. A semiconductor light emitting deviceaccording to claim 1, wherein the recess has a depth of 2 micrometers orgreater.
 4. A semiconductor light emitting device according to claim 1,wherein the first plane makes an angle of 10 to 80 degrees with thefirst major surface.
 5. A semiconductor light emitting device accordingto claim 1, wherein the second plane makes an angle of 10 to 80 degreeswith the first major surface.
 6. A semiconductor light emitting deviceaccording to claim 1, wherein the substrate is made of GaP, and thelight emitting layer is made of In_(x)Ga_(y)Al_(1−x−y)P, where 0≦x≦1,0≦y≦1, and (x+y)≦1.
 7. A semiconductor light emitting device accordingto claim 1, wherein the substrate is made of sapphire, and the lightemitting layer is made of In_(z)Ga_(w)Al_(1−z−w)N, where 0≦z≦1, 0≦w≦1,and (z+w)≦1.
 8. A semiconductor light emitting apparatus, comprising: apackaging member; a semiconductor light emitting device mounted on thepackaging member; and sealing resin sealing the semiconductor lightemitting device, the semiconductor light emitting device including: asubstrate having first and second major surfaces and being translucentto light in a first wavelength band; and a semiconductor stacked bodyprovided on the first major surface and including a light emitting layerthat emits light in the first wavelength band, a side face of thesubstrate having a recess, the recess extending in parallel to the firstand second major surfaces, the recess being formed all around thesubstrate, a cross section located between the first and second majorsurfaces being smaller than the first and second major surfaces, therecess being composed of a combination of a first plane extendingobliquely downward and a second plane extending obliquely upward, andthe first and second major surfaces having an equal size.
 9. Asemiconductor light emitting apparatus according to claim 8, furthercomprising a reflector configured to reflect light radiated from therecess.
 10. A semiconductor light emitting apparatus according to claim8, wherein the recess is composed of a curved surface.
 11. Asemiconductor light emitting apparatus according to claim 8, wherein arough surface is provided on at least a portion of the recess.
 12. Asemiconductor light emitting device according to claim 1, wherein theside face of the substrate has a first surface which is provided betweenthe recess and the first major surface, and is substantiallyperpendicular to the first major surface.
 13. A semiconductor lightemitting device according to claim 8, wherein the side face of thesubstrate has a first surface which is provided between the recess andthe first major surface, and is substantially perpendicular to the firstmajor surface.
 14. A semiconductor light emitting device according toclaim 12, wherein the side face of the substrate further has a secondsurface which is provided between the recess and the second majorsurface, and is substantially perpendicular to the second major surface.15. A semiconductor light emitting device according to claim 13, whereinthe side face of the substrate further has a second surface which isprovided between the recess and the second major surface, and issubstantially perpendicular to the second major surface.
 16. Asemiconductor light emitting device comprising: a substrate having firstand second major surfaces and being translucent to light in a firstwavelength band; and a semiconductor stacked body provided on the firstmajor surface and including a light emitting layer that emits light inthe first wavelength band, a side face of the substrate having a recess,the recess extending in parallel to the first and second major surfaces,the recess being formed all around the substrate, a cross sectionlocated between the first and second major surfaces being smaller thanthe first and second major surfaces, the recess is composed of a curvedsurface, and the first and second major surfaces having an equal size.